Microwave radiating applicator with reduced sensitivity to surrounding media

ABSTRACT

A microwave energy applicator radiating uniformly all around the applicator that maintains high efficiency Voltage Standing Wave Ratio (V.S.W.R.) for surrounding media of dielectric constants varying from about 1 to about 80. In a particular embodiment, the high efficiency V.S.W.R. is less than about 1.3:1. The applicator can include a circular polarizer connectable to a dielectric waveguide radiator. The radiator can be substantially solid and include a substantially circular outer cross-section that tapers to an end. In one embodiment, the radiator includes a conical void formed in a dielectric entry section.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/471,401, filed May 16, 2003, the entire teachings of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

It is often a requirement to place an energy applicator in an area wherethe surrounding media may change with time and/or application of power.This occurs, for example, in soil remediation and heating of viscous oildeposits, where the applicator may be surrounded by air, gas, water, orhydrocarbons, individually or in mixtures. The transmission ofsubstantial amounts of microwave power is most efficiently done by awaveguide. However, this requires sealing and pressurization of itselfand the applicator to prevent inflow of the items being heated.

The previous approaches have used slotted waveguide applicators. Slotsare typically on the broad wall of the waveguide. See, for example, W.Rueggeberg in “A Multislotted Waveguide Antenna for High-PoweredMicrowave Heating Systems”, IEEE Transactions on Industry Applications,Vol. 1A-16, Number 6, pp 809-813, November/December 1980.

SUMMARY OF THE INVENTION

However, radiation from a slot in a metal waveguide varies as a functionof the dielectric characteristics of the surrounding media. This meansthat a slotted radiator with a high efficiency (low Voltage StandingWave Ratio (V.S.W.R.)) in air will typically have a poor efficiency(high V.S.W.R.) in water. Slotted radiators must be sealed if fouling isto be avoided.

A further problem for radiators using a rectangular waveguide is thatthe heating effects are not uniform around the applicator because therectangular guide includes four planar surfaces. Whether the slots arein the broad walls or the narrow walls of the waveguide, the radiationis essentially radiating with the maximum intensity perpendicular to theplane of the surface in which the slot is cut.

An embodiment of the invention provides for a uniform radiation aroundan applicator while maintaining high efficiency for a wide range ofsurrounding media.

A microwave energy applicator is provided for radiating uniformly allaround the applicator. The applicator can provide a relatively uniformradiation to a variety of surrounding media and maintains highefficiency Voltage Standing Wave Ratio (V.S.W.R.) for media surroundingthe applicator having dielectric constants from about 1 to about 80. Ina particular embodiment, the high efficiency V.S.W.R. is less than about1.3:1. The even energy spread radially throughout 360 degrees around theapplicator is achieved by maintaining circular symmetry throughout theradiator, and launching circularly polarized microwaves into theradiator from a round waveguide. The circularly polarized waves in theround waveguide are produced in one embodiment using arectangular-to-round waveguide transformer and a cylindrical sectioncontaining an asymmetrical insert or inserts.

The applicator includes a circular polarizer or guide connectable to adielectric waveguide radiator, which can be substantially solid. In oneembodiment, the radiator includes a conical void in a dielectric entrysection to provide tapered matching from the air-(or other suitable gas)filled circular guide to the solid dielectric waveguide. The radiatorcan include a substantially circular outer cross-section that tapers toan end. In a specific embodiment, the radiating section of the radiatoris polypropylene.

The polarizer can include one or more asymmetrical inserts for providinga circularly polarized microwave energy output given a linearlypolarized microwave input.

A microwave energy applicator is provided in accordance with otheraspects of the present invention comprising a circular polarizerconnectable to a dielectric waveguide radiator. The radiator can includea substantially circular outer cross-section that tapers to an end and aconical void formed in a dielectric entry section. A flange isconnectable between the polarizer and the radiator.

In one embodiment, the radiator includes polypropylene and issubstantially solid. The polarizer can include one or more asymmetricalinserts for providing a circularly polarized microwave energy outputgiven a linearly polarized microwave input. In a particular embodiment,the polarizer includes a substantially circular outer cross-section.

A microwave energy applicator is further provided comprising a circularpolarizer connectable to a substantially solid dielectric waveguideradiator. The radiator can include a conical void formed in a dielectricentry section. The dielectric material for the radiator is selected sothat for dimensions compatible with the high-power circular waveguidefeed, it functions as a leaky waveguide. In this manner, the radiatorradiates from its sides while continuing some of the energy forward. Theleakage rate from the waveguide varies depending on its surroundings.The resulting radiation is uniform radially at any point and is spreadrelatively uniformly along the length.

The applicator can provide a relatively uniform radiation to a varietyof surrounding media and maintains high efficiency Voltage Standing WaveRatio (V.S.W.R.) for media surrounding the applicator having dielectricconstants from about 1 to about 80. In a particular embodiment, the highefficiency V.S.W.R. is less than about 1.3:1.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of various embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a perspective view of a microwave applicator according to anembodiment of the present invention.

FIG. 2 is a longitudinal cross-sectional view of the applicator.

FIG. 3 is an end view of the applicator.

DETAILED DESCRIPTION OF THE INVENTION

A description of various embodiments of the invention follows.

FIG. 1 is a perspective view of the components of a microwave applicator10 constructed in accordance with principles of the present invention.The applicator 10 includes a circular polarizer section 12, a flange 14,a sealing ring or clamp plate 16, a rectangular-to-round transformer 18,and a dielectric waveguide radiator 20. The applicator 10 is ofparticular use in heating a surrounding media that may change over timeor be unknown. This situation can occur in soil remediation and heatingof viscous oil deposits that occur in oil deposit exploration. In suchenvironments, the applicator 10 may be surrounded by, for example, air,gas, water, hydrocarbons, and soil materials individually and/or inmixtures.

Furthermore, in cold weather environments, it is possible that thesurrounding media may actually change with the application of microwaveenergy. Prior to application of the energy, the surrounding media mayinclude frozen water, ice and oil mixture; however, once microwaveenergy begins to be applied in the surrounding media, the ice meltsthereby forming water. The media then changes its composition and itsability to absorb microwave energy.

FIG. 2 is a longitudinal cross-sectional view of the applicator 10. Thescale above FIG. 2 is in inches. This embodiment is for operation atabout 915 MHz using a dielectric radiator 20 made of polypropylene. Itcan be seen here more particularly that the circular polarizer 12contains a cylindrical section piece having one or more asymmetricalinserts 22 and 24. The circular polarizer 12 provides a circularlypolarized microwave output when a linearly polarized wave is supplied toit through the rectangular-to-round transformer 18 at a 45 degree angleto the asymmetrical insert or inserts 22 and 24.

This method to provide a circularly polarized wave is the same asdescribed in U.S. Pat. No. 6,034,362 issued to Alton, entitled“Circularly Polarized Microwave Energy Feed” in March 2000 and assignedto the Ferrite Company, and also in U.S. Pat. No. 6,274,858 issued toAlton entitled “Bends in a Compact Circularly Polarized Microwave Feed”in August 2001, also assigned to the Ferrite Company.

In one embodiment, the dielectric waveguide radiator 20 is generallycylindrical in shape, and has circular symmetry about a center axis. Aconical void 28 is formed in a dielectric entry section. An exteriortaper portion 32 carries from a midsection out towards the tip or end30. In a particular embodiment, the radiator 20 is substantially solid.

For high-power transmission, to avoid overheating of the dielectricradiators, which can cause thermal stress and damage, a low lossdielectric, such as polypropylene, can be used. When a solid dielectricwaveguide is made of polypropylene, which can have a dielectric constantof about 2.2, and with a diameter close to that of the single mode TE₁₁circular energy waveguide, the propagation is leaky even when surroundedby air. Energy containment in a dielectric waveguide relies on a largerdielectric constant of the waveguide compared to its surroundings so airis the worst case for radiation.

The diameter of the solid radiator 20 was selected to allow justsufficient radiation in air to have a good match (low reflection) forfour foot long dielectric radiators. This was thought to be compatiblewith achieving suitable energy densities in soil remediationapplications where the heating is required to be spread to thesurroundings without excessive hot spots.

Tapers can be provided at each end of the solid dielectric portion 20.One is a conical void 28 inside the radiator 20, and provides a gradualimpedance transition for the circular metal waveguide 12 to the soliddielectric guide 20. The taper 32 at the front to the rounded end 30provides a gradual transition, from a portion of the waveguide that isleaking energy radiating while transporting it, to no waveguide. As thediameter of the dielectric radiator 20 decreases towards the end 30, itsability to contain energy decreases resulting in increased radiation.

The radiation is radially uniform around the dielectric radiator 20 atsubstantially all cross-sections. The distribution along the radiator 20length shifts for different surrounding media. For air, the radiation isrelatively uniform along the length while for higher dielectricconstants, such as water, the radiation is almost complete at the startof the taper 32.

The leaky dielectric waveguide radiator 20 is connected to the polarizer12 by a metal flange 14 with a bolt-on clamp plate 16. This provides anO-ring pressure seal to the radiator 20.

The conical void 28 inside the radiator 20 provides a match to the emptyor hollow circular polarizer 12.

The outer diameter of the radiator 20 is tapered 32 to provide effectiveleakage radiation where the tubular piece becomes solid. In this manner,the end 30 can radiate the remaining microwave energy uniformly over ashort length.

In a particular embodiment, the dielectric material that forms radiator20 includes polypropylene, although other low dielectric loss materialsare suitable.

While this invention has been particularly shown and described withreferences to various embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A microwave energy device comprising: a dielectric waveguideapplicator, having an applicator input and applicator end, the waveguidealso having a generally circular cross section, and the waveguide beingformed from a solid dielectric material along at least fifty percent(50%) of its overall length, the waveguide further comprising: a centerportion, having a substantially constant outer diameter, and solidinterior portion; an entry portion, disposed adjacent the centerportion, and having an outer diameter that tapers from a firstrelatively larger outer diameter adjacent the applicator input, to afirst relatively smaller outer diameter adjacent the center portion, theentry portion also having a tapered conical void formed within thatpresents a decrease in void diameter with distance from the applicatorinput; and an exit taper portion, disposed on a side of the centerportion opposite the entry portion, the exit taper portion having asolid interior portion, and having an outer diameter that tapers from asecond relatively larger outer diameter adjacent the center portion to asecond relatively smaller outer diameter adjacent the applicator end. 2.A microwave energy applicator as in claim 1, providing radiationuniformly all around the applicator that maintains high efficiencyVoltage Standing Wave Ratio (V.S.W.R.) for surrounding media ofdielectric constants varying from about 1 to about
 80. 3. The applicatorof claim 2, wherein the high efficiency V.S.W.R. is less than about1.3:1.
 4. The applicator of claim 1, wherein the dielectric materialincludes polypropylene.
 5. The applicator of claim 1, wherein theapplicator provides a relatively uniform radiation to a variety ofsurrounding media.
 6. The microwave energy applicator device of claim 1additionally wherein the tapered conical void further extends into afirst part of the center portion, such that a thickness of the anexterior wall of the first part of the center portion increases withdistance from the applicator input.
 7. The microwave device of claim 1additionally comprising: a circular polarized, coupled to the waveguideapplicator, for applying circulatory polarized microwave energy thereto.8. The applicator of claim 7, wherein the conical void has a taperselected for providing an impedance match between the waveguide radiatorand the polarizer.
 9. The applicator of claim 7, wherein a flange isconnected between the circular polarizer and the waveguide radiator. 10.The applicator of claim 7, wherein the circular polarizer includes oneor more asymmetrical inserts for providing a circularly polarizedmicrowave energy output from a linearly polarized microwave inputsignal.